Planetary gear train of automatic transmission for vehicles

ABSTRACT

A planetary gear train of claim of an automatic transmission for a vehicle may include an input shaft for receiving an engine torque, an output shaft for outputting a shifted torque, a first planetary gear set, a second planetary gear set, a third planetary gear set, a fourth planetary gear set, a first shaft, a second shaft directly connected with the input shaft, a third shaft, a fourth shaft, a fifth shaft selectively connectable with each of the first shaft and the third shaft, a sixth shaft selectively connectable with the third shaft, a seventh shaft, and an eighth shaft selectively connectable with the third shaft, and directly connected with the output shaft.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No.10-2016-0033000, filed Mar. 18, 2016, the entire contents of which isincorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an automatic transmission for avehicle. More particularly, the present invention relates to a planetarygear train of an automatic transmission of a vehicle that improves powerdelivery performance and reduces fuel consumption by achieving tenforward speed stages using a minimum number of constituent elements.

Description of Related Art

Research on realizing more shift-stages of an automatic transmission hasbeen undertaken to achieve enhancement of fuel consumption and betterdrivability, and recent increases in oil prices are triggering stiffcompetition in enhancing fuel consumption of a vehicle.

In this sense, research on an engine has been undertaken to achieveweight reduction and to enhance fuel consumption by so-called downsizingand research on an automatic transmission has been performed tosimultaneously provide better drivability and fuel consumption byachieving more shift stages.

However, in the automatic transmission, as the number of speed stagesincrease, the number of internal components (particularly, planetarygear sets) increase, which may deteriorate installability and/or powerflow efficiency and may increase production cost, and weight.

Therefore, in order to maximally enhance fuel consumption of anautomatic transmission having more shift stages, it is important forbetter efficiency to be derived by a smaller number of parts.

In this respect, an eight-speed automatic transmission has been recentlyintroduced, and a planetary gear train for an automatic transmissionenabling more shift stages is under investigation.

An automatic transmission of eight or more shift-stages typicallyincludes three to four planetary gear sets and five to six controlelements (frictional elements), and may easily become lengthy, therebydeteriorating installability.

In this regard, disposing planetary gear sets in parallel or employingdog clutches instead of wet-type control elements has been attempted.However, such an arrangement is not widely applicable, and using dogclutches may easily deteriorate shift-feel.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and should not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing aplanetary gear train of an automatic transmission for a vehicle havingadvantages of obtaining shift-stages of at least ten forward speeds andat least one reverse speed by minimal number of parts, improving powerdelivery performance and fuel consumption by multiple speed-stages of anautomatic transmission, and improving driving stability of a vehicle byutilizing a low rotation speed of an engine.

According to various aspects of the present invention, a planetary geartrain of claim of an automatic transmission for a vehicle may include aninput shaft for receiving an engine torque, an output shaft foroutputting a shifted torque, a first planetary gear set including first,second, and third rotation elements, a second planetary gear setincluding fourth, fifth, and sixth rotation elements, a third planetarygear set including seventh, eighth, and ninth rotation elements, afourth planetary gear set including tenth, eleventh, and twelfthrotation elements, a first shaft connected with the first rotationelement, a second shaft interconnecting the second rotation element, thefourth rotation element, and the eighth rotation element, and directlyconnected with the input shaft, a third shaft connected with the thirdrotation element, a fourth shaft interconnecting the fifth rotationelement and the twelfth rotation element, a fifth shaft connected withthe sixth rotation element, and selectively connectable with each of thefirst shaft and the third shaft, a sixth shaft interconnecting theseventh rotation element and the tenth rotation element, and selectivelyconnectable with the third shaft, a seventh shaft connected with theninth rotation element, and an eighth shaft connected with the eleventhrotation element, selectively connectable with the third shaft, anddirectly connected with the output shaft.

The sixth shaft and the seventh shaft may each be selectivelyconnectable with a transmission housing.

The first, second, and third rotation elements may be a first sun gear,a first planet carrier, and a first ring gear, the fourth, fifth, andsixth rotation elements may be a second sun gear, a second planetcarrier, and a second ring gear, the seventh, eighth, and ninth rotationelements may be a third sun gear, a third planet carrier, and a thirdring gear, and the tenth, eleventh, and twelfth rotation elements may bea fourth sun gear, a fourth planet carrier, and a fourth ring gear.

The planetary gear train may further include a first clutch selectivelyconnecting the third shaft and the eighth shaft, a second clutchselectively connecting the first shaft and the fifth shaft, a thirdclutch selectively connecting the third shaft and the fifth shaft, afourth clutch selectively connecting the third shaft and the sixthshaft, a first brake selectively connecting the sixth shaft and thetransmission housing, and a second brake selectively connecting theseventh shaft and the transmission housing.

According to various aspects of the present invention, a planetary geartrain of claim of an automatic transmission for a vehicle may include aninput shaft for receiving an engine torque, an output shaft foroutputting a shifted torque, a first planetary gear set including first,second, and third rotation elements, a second planetary gear setincluding fourth, fifth, and sixth rotation elements, a third planetarygear set including seventh, eighth, and ninth rotation elements, and afourth planetary gear set including tenth, eleventh, and twelfthrotation elements, in which the input shaft may be directly connectedwith the second rotation element, the output shaft may be directlyconnected with the eleventh rotation element, the second rotationelement may be directly connected with the fourth rotation element andthe eighth rotation element, the fifth rotation element may be directlyconnected with the twelfth rotation element, the sixth rotation elementmay be selectively connectable with each of the first rotation elementand the third rotation element, the seventh rotation element may beselectively connectable with the third rotation element, and the tenthrotation element may be directly connected with the seventh rotationelement.

The seventh rotation element and the ninth rotation element may each beselectively connectable with a transmission housing.

The planetary gear train may further include a first clutch selectivelyconnecting the third rotation element and the eleventh rotation element,a second clutch selectively connecting the first rotation element andthe sixth rotation element, a third clutch selectively connecting thethird rotation element and the sixth rotation element, a fourth clutchselectively connecting the third rotation element and the seventhrotation element, a first brake selectively connecting the seventhrotation element and the transmission housing, and a second brakeselectively connecting the ninth rotation element and the transmissionhousing.

Speed shift-stages implemented by selectively operating the first,second, third and fourth clutches and the first and second brakes mayinclude a forward first speed shift-stage, implemented by operating thethird and fourth clutches, and the first brake, a forward second speedshift-stage, implemented by operating the first and third clutches, andthe first brake, a forward third speed shift-stage, implemented byoperating the second and third clutches, and the first brake, a forwardfourth speed shift-stage, implemented by operating the first and secondclutches, and the first brake, a forward fifth speed shift-stage,implemented by operating the first, second and third clutches, a forwardsixth speed shift-stage, implemented by operating the first and secondclutches, and the second brake, a forward seventh speed shift-stage,implemented by operating the second and third clutches, and the secondbrake, a forward eighth speed shift-stage, implemented by operating thefirst and third clutches, and the second brake, a forward ninth speedshift-stage, implemented by operating the third and fourth clutches, andthe second brake, a forward tenth speed shift-stage, implemented byoperating the first and fourth clutches, and the second brake, and areverse-speed shift-stage, implemented by operating the second andfourth clutches, and the second brake.

According to various embodiments of the present invention, shift-stagesof at least ten forward speeds and at least one reverse speed arerealized by combination of four planetary gear sets and six controlelements.

In addition, a planetary gear train according to various embodiments ofthe present invention substantially improves driving stability byrealizing shift-stages appropriate for rotation speed of an engine dueto multiple speed-stages of an automatic transmission.

Furthermore, a planetary gear train according to various embodiments ofthe present invention maximizes engine driving efficiency by multiplespeed-stages of an automatic transmission, and improves power deliveryperformance and fuel consumption.

It is understood that the term “vehicle” or “vehicular” or other similarterms as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g., fuel derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example, bothgasoline-powered and electric-powered vehicles.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a planetary gear train according tovarious embodiments of the present invention.

FIG. 2 is an operational chart for respective control elements atrespective shift-stages in the planetary gear train according to variousembodiments of the present invention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that the present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

FIG. 1 is a schematic diagram of a planetary gear train according tovarious embodiments of the present invention.

Referring to FIG. 1, a planetary gear train according to variousembodiments of the present invention includes first, second, third, andfourth planetary gear set PG1, PG2, PG3, and PG4, arranged on a sameaxis, an input shaft IS, an output shaft OS, eight shafts TM1 to TM8interconnecting rotation elements of the first, second, third, andfourth planetary gear sets PG1, PG2, PG3, and PG4, four clutches C1 toC4 and two brakes B1 and B2 as control elements, and a transmissionhousing H.

Torque input from the input shaft IS is shifted by cooperative operationof the first, second, third, and fourth planetary gear sets PG1, PG2,PG3, and PG4, and then output through the output shaft OS.

The planetary gear sets are arranged in the order of first, second,third, and fourth planetary gear sets PG1, PG2, PG3, and PG4, from anengine side.

The input shaft IS is an input member and the torque from a crankshaftof an engine is input into the input shaft IS, after beingtorque-converted through a torque converter.

The output shaft OS is an output member, and being arranged on a sameaxis with the input shaft IS, delivers a shifted driving torque to adrive shaft through a differential apparatus.

The first planetary gear set PG1 is a single pinion planetary gear set,and includes a first planet carrier PC1 that supports first pinion gearP1 externally engaged with the first sun gear S1, and a first ring gearR1 that is internally engaged with the first pinion gear P1. The firstsun gear S1 acts as a first rotation element N1, the first planetcarrier PC1 acts as a second rotation element N2, and the first ringgear R1 acts as a third rotation element N3.

The second planetary gear set PG2 is a single pinion planetary gear set,and includes a second planet carrier PC2 that supports second piniongear P2 externally engaged with the second sun gear S2, and a secondring gear R2 that is internally engaged with the second pinion gear P2.The second sun gear S2 acts as a fourth rotation element N4, the secondplanet carrier PC2 acts as a fifth rotation element N4, and the secondring gear R2 acts as a sixth rotation element N6.

The third planetary gear set PG3 is a single pinion planetary gear set,and includes a third planet carrier PC3 that supports third pinion gearP3 externally engaged with the third sun gear S3, and a third ring gearR3 that is internally engaged with the third pinion gear P3. The thirdsun gear S3 acts as a seventh rotation element N7, the third planetcarrier PC3 acts as an eighth rotation element N8, and the third ringgear R3 acts as a ninth rotation element N9.

The fourth planetary gear set PG4 is a single pinion planetary gear set,and includes a fourth planet carrier PC4 that supports fourth piniongear P4 externally engaged with the fourth sun gear S4, and a fourthring gear R4 that is internally engaged with the fourth pinion gear P4.The fourth sun gear S4 acts as a tenth rotation element N10, the fourthplanet carrier PC4 acts as a eleventh rotation element N11, and thefourth ring gear R4 acts as a twelfth rotation element N12.

In the first, second, third, and fourth planetary gear set PG1, PG2,PG3, and PG4, the second rotation element N2 is directly connected withthe fourth rotation element N4 and the eighth rotation element N8, thefifth rotation element N5 is directly connected with the twelfthrotation element N12, and the seventh rotation element N7 is directlyconnected with the tenth rotation element N10, by eight shafts TM1 toTM8.

The eight shafts TM1 to TM8 are hereinafter described in detail.

Each of the eight shafts TM1 to TM8 may be a rotation member thatdirectly interconnects the input and output shafts and rotation elementsof the planetary gear sets PG1, PG2, PG3, and PG4, or may be a fixedmember fixed to the transmission housing H.

The first shaft TM1 is connected with the first rotation element N1 (thefirst sun gear S1).

The second shaft TM2 directly connects the second rotation element N2(the first planet carrier PC1), the fourth rotation element N4 (thesecond sun gear S2), and the eighth rotation element N8 (the thirdplanet carrier PC3), and directly connected with the input shaft IS,thereby continuously acting as an input element.

The third shaft TM3 is connected with the third rotation element N3 (thefirst ring gear R1).

The fourth shaft TM4 directly connects the fifth rotation element N5(the second planet carrier PC2) and the twelfth rotation element N12(the fourth ring gear R4).

The fifth TM5 is connected with the sixth rotation element N6 (thesecond ring gear R2), is selectively connectable with the first shaftTM1, and is selectively connectable with the third TM3.

The sixth TM6 directly connects the seventh rotation element N7 (thethird sun gear S3) and the tenth rotation element N10 (the fourth sungear S4), is selectively connectable with the third shaft TM3, and isselectively connectable with the transmission housing H, therebyselectively acting as a fixed element.

The seventh shaft TM7 is connected with the ninth rotation element N9(the third ring gear R3), and is selectively connectable with thetransmission housing H, thereby selectively acting as a fixed element.

The eighth shaft TM8 is connected with the eleventh rotation element N11(the fourth planet carrier PC4), is selectively connectable with thethird shaft TM3, and is directly connected with the output shaft OS,thereby continuously acting as an output element.

The eight shafts TM1 to TM8, the input shaft IS, and the output shaft OSmay be selectively interconnected with one another by control elementsof four clutches C1, C2, C3, and C4.

The eight shafts TM1 to TM8 may be selectively connectable with thetransmission housing H, by control elements of two brakes B1 and B2.

The four clutches C1 to C4 and the two brakes B1 and B2 are arranged asfollows.

The first clutch C1 is arranged between the third shaft TM3 and theeighth shaft TM8, and selectively connects the third shaft TM3 and theeighth shaft TM8 connected with the output shaft OS thereby controllingpower delivery therebetween.

The second clutch C2 is arranged between the first shaft TM1 and thefifth shaft TM5, and selectively connects the first shaft TM1 and thefifth shaft TM5 connected with the output shaft OS thereby controllingpower delivery therebetween.

The third clutch C3 is arranged between the third shaft TM3 and thefifth shaft TM5, and selectively connects the third shaft TM3 and thefifth shaft TM5 connected with the output shaft OS thereby controllingpower delivery therebetween.

The fourth clutch C4 is arranged between the third shaft TM3 and sixthshaft TM6, and selectively connects the third shaft TM3 and sixth shaftTM6 connected with the output shaft OS thereby controlling powerdelivery therebetween.

The first brake B1 is arranged between the sixth TM6 and thetransmission housing H, and selectively connects the sixth shaft TM6 tothe transmission housing H.

The second brake B2 is arranged between the seventh shaft TM7 and thetransmission housing H, and selectively connects the seventh shaft TM7to the transmission housing H.

The respective control elements of the first, second, third, and fourthclutches C1, C2, C3, and C4 and the first and second brakes B1 and B2may be realized as multi-plate hydraulic pressure friction devices thatare frictionally engaged by hydraulic pressure.

FIG. 2 is an operational chart for respective control elements atrespective shift-stages in a planetary gear train according to variousembodiments of the present invention.

Referring to FIG. 2, a planetary gear train according to variousembodiments of the present invention realizes ten forward speeds and onereverse speed by operating three control elements among the first,second, third, and fourth clutches C1, C2, C3, and C4 and the first andsecond brakes B1 and B2 at respective shift-stages.

In the forward first speed shift-stage D1, the third and fourth clutchesC3 and C4 and the first brake B1 are operated.

As a result, the third shaft TM3 is connected with the fifth shaft TM5by the operation of the third clutch C3, and the third shaft TM3 isconnected with the sixth shaft TM6 by the operation of the fourth clutchC4. In this state, the torque of the input shaft IS is input to thesecond shaft TM2.

In addition, the sixth shaft TM6 acts as a fixed element by theoperation of the first brake B1, thereby realizing the forward firstspeed by cooperative operation of respective shafts and outputting ashifted torque to the output shaft OS connected with the eighth shaftTM8.

In the forward second speed shift-stage D2, the first and third clutchesC1 and C3 and the first brake B1 are operated.

As a result, the third shaft TM3 is connected with the eighth shaft TM8by the operation of the first clutch C1, and the third shaft TM3 isconnected with the fifth shaft TM5 by the operation of the third clutchC3. In this state, the torque of the input shaft IS is input to thesecond shaft TM2.

In addition, the sixth shaft TM6 acts as a fixed element by theoperation of the first brake B1, thereby realizing the forward secondspeed by cooperative operation of respective shafts and outputting ashifted torque to the output shaft OS connected with the eighth shaftTM8.

In the forward third speed shift-stage D3, the second and third clutchesC2 and C3 and the first brake B1 are operated.

As a result, the first shaft TM1 is connected with the fifth shaft TM5by the operation of the second clutch C2, and the third shaft TM3 isconnected with the fifth shaft TM5 by the operation of the third clutchC3. In this state, the torque of the input shaft IS is input to thesecond shaft TM2.

In addition, the sixth shaft TM6 acts as a fixed element by theoperation of the first brake B1, thereby realizing the forward thirdspeed by cooperative operation of respective shafts and outputting ashifted torque to the output shaft OS connected with the eighth shaftTM8.

In the forward fourth speed shift-stage D4, the first and secondclutches C1 and C2 and the first brake B1 are operated.

As a result, the third shaft TM3 is connected with the eighth shaft TM8by the operation of the first clutch C1, and the first shaft TM1 isconnected with the fifth shaft TM5 by the operation of the second clutchC2. In this state, the torque of the input shaft IS is input to thesecond shaft TM2.

In addition, the sixth shaft TM6 acts as a fixed element by theoperation of the first brake B1, thereby realizing the forward fourthspeed by cooperative operation of respective shafts and outputting ashifted torque to the output shaft OS connected with the eighth shaftTM8.

In the forward fifth speed shift-stage D5, the first, second, and thirdclutches C1, C2 and C3 are operated.

As a result, the third shaft TM3 is connected with the eighth shaft TM8by the operation of the first clutch C1, the first shaft TM1 isconnected with the fifth shaft TM5 by the operation of the second clutchC2, and the third shaft TM3 is connected with the fifth shaft TM5 by theoperation of the third clutch C3. In this state, the torque of the inputshaft IS is input to the second shaft TM2.

In this case, entire planetary gear sets PG1, PG2, PG3, and PG4integrally rotate, and a torque is output as input, thereby forming theforward fifth speed and outputting the input torque to the output shaftOS connected with the eighth shaft TM8.

In the forward sixth speed shift-stage D6, the first and second clutchesC1 and C2 and the second brake B2 are operated.

As a result, the third shaft TM3 is connected with the eighth shaft TM8by the operation of the first clutch C1, and the first shaft TM1 isconnected with the fifth shaft TM5 by the operation of the second clutchC2. In this state, the torque of the input shaft IS is input to thesecond shaft TM2.

In addition, the seventh shaft TM7 acts as a fixed element by theoperation of the second brake B2, thereby realizing the forward sixthspeed by cooperative operation of respective shafts and outputting ashifted torque to the output shaft OS connected with the eighth shaftTM8.

In the forward seventh speed shift-stage D7, the second and thirdclutches C2 and C3 and the second brake B2 are operated.

As a result, the first shaft TM1 is connected with the fifth shaft TM5by the operation of the second clutch C2, and the third shaft TM3 isconnected with the fifth shaft TM5 by the operation of the third clutchC3. In this state, the torque of the input shaft IS is input to thesecond shaft TM2.

In addition, the seventh shaft TM7 acts as a fixed element by theoperation of the second brake B2, thereby realizing the forward seventhspeed by cooperative operation of respective shafts and outputting ashifted torque to the output shaft OS connected with the eighth shaftTM8.

In the forward eighth speed shift-stage D8, the first and third clutchesC1 and C3 and the second brake B2 are operated.

As a result, the third shaft TM3 is connected with the eighth shaft TM8by the operation of the first clutch C1, and the third shaft TM3 isconnected with the fifth shaft TM5 by the operation of the third clutchC3. In this state, the torque of the input shaft IS is input to thesecond shaft TM2.

In addition, the seventh shaft TM7 acts as a fixed element by theoperation of the second brake B2, thereby realizing the forward eighthspeed by cooperative operation of respective shafts and outputting ashifted torque to the output shaft OS connected with the eighth shaftTM8.

In the forward ninth speed shift-stage D9, the third and fourth clutchesC3 and C4 and the second brake B2 are operated.

As a result, the third shaft TM3 is connected with the fifth shaft TM5by the operation of the third clutch C3, and the third shaft TM3 isconnected with the sixth shaft TM6 by the operation of the fourth clutchC4. In this state, the torque of the input shaft IS is input to thesecond shaft TM2.

In addition, the seventh shaft TM7 acts as a fixed element by theoperation of the second brake B2, thereby realizing the forward ninthspeed by cooperative operation of respective shafts and outputting ashifted torque to the output shaft OS connected with the eighth shaftTM8.

In the forward tenth speed shift-stage D10, the first and fourthclutches C1 and C4 and the second brake B2 are operated.

As a result, the third shaft TM3 is connected with the eighth shaft TM8by the operation of the first clutch C1, and the third shaft TM3 isconnected with the sixth shaft TM6 by the operation of the fourth clutchC4. In this state, the torque of the input shaft IS is input to thesecond shaft TM2.

In addition, the seventh shaft TM7 acts as a fixed element by theoperation of the second brake B2, thereby realizing the forward tenthspeed by cooperative operation of respective shafts and outputting ashifted torque to the output shaft OS connected with the eighth shaftTM8.

In the reverse speed REV, the second and fourth clutches C2 and C4, andthe second brake B2 are operated.

As a result, the first shaft TM1 is connected with the fifth shaft TM5by the operation of the second clutch C2, and the third shaft TM3 isconnected with the sixth shaft TM6 by the operation of the fourth clutchC4. In this state, the torque of the input shaft IS is input to thesecond shaft TM2.

In addition, the seventh shaft TM7 acts as a fixed element by theoperation of the second brake B2, thereby realizing the reverse speed bycooperative operation of respective shafts and outputting a shiftedtorque to the output shaft OS connected with the eighth shaft TM8.

As described above, a planetary gear train according to variousembodiments of the present invention realizes at least ten forwardspeeds and at least one reverse speed by operating four planetary gearsets PG1, PG2, PG3, and PG4 by controlling the four clutches C1, C2, C3,and C4 and the two brakes B1 and B2.

In addition, a planetary gear train according to various embodiments ofthe present invention realizes shift stages appropriate for rotationspeed of an engine due to multiple speed-stages of an automatictransmission and improves driving stability of a vehicle by utilizing alow rotation speed of an engine.

Furthermore, a planetary gear train according to various embodiments ofthe present invention maximizes engine driving efficiency by multiplespeed-stages of an automatic transmission, and improves power deliveryperformance and fuel consumption.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

What is claimed is:
 1. A planetary gear train of claim of an automatictransmission for a vehicle, comprising: an input shaft for receiving anengine torque; an output shaft for outputting a shifted torque; a firstplanetary gear set including a first rotation element, a second rotationelement, and a third rotation element; a second planetary gear setincluding a fourth rotation element, a fifth rotation element, and asixth rotation element; a third planetary gear set including a seventhrotation element, an eighth rotation element, and a ninth rotationelement; a fourth planetary gear set including a tenth rotation element,an eleventh rotation element, and a twelfth rotation element; a firstshaft connected with the first rotation element; a second shaftinterconnecting the second rotation element, the fourth rotationelement, and the eighth rotation element, and directly connected withthe input shaft; a third shaft connected with the third rotationelement; a fourth shaft interconnecting the fifth rotation element andthe twelfth rotation element; a fifth shaft connected with the sixthrotation element, and selectively connectable with each of the firstshaft and the third shaft; a sixth shaft interconnecting the seventhrotation element and the tenth rotation element, and selectivelyconnectable with the third shaft; a seventh shaft connected with theninth rotation element; and an eighth shaft connected with the eleventhrotation element, selectively connectable with the third shaft, anddirectly connected with the output shaft.
 2. The planetary gear train ofclaim 1, wherein the sixth shaft and the seventh shaft are eachselectively connectable with a transmission housing.
 3. The planetarygear train of claim 1, wherein the first rotation element, the secondrotation element, and the third rotation element comprise a first sungear, a first planet carrier, and a first ring gear; the fourth rotationelement, the fifth rotation element, and the sixth rotation elementcomprise a second sun gear, a second planet carrier, and a second ringgear; the seventh rotation element, the eighth rotation element, and theninth rotation element comprise a third sun gear, a third planetcarrier, and a third ring gear; and the tenth rotation element, theeleventh rotation element, and the twelfth rotation element comprise afourth sun gear, a fourth planet carrier, and a fourth ring gear.
 4. Theplanetary gear train of claim 2, further comprising: a first clutchselectively connecting the third shaft and the eighth shaft; a secondclutch selectively connecting the first shaft and the fifth shaft; athird clutch selectively connecting the third shaft and the fifth shaft;a fourth clutch selectively connecting the third shaft and the sixthshaft; a first brake selectively connecting the sixth shaft and thetransmission housing; and a second brake selectively connecting theseventh shaft and the transmission housing.
 5. A planetary gear train ofclaim of an automatic transmission for a vehicle, comprising: an inputshaft for receiving an engine torque; an output shaft for outputting ashifted torque; a first planetary gear set including a first rotationelement, a second rotation element, and a third rotation element; asecond planetary gear set including a fourth rotation element, a fifthrotation element, and a sixth rotation element; a third planetary gearset including a seventh rotation element, an eighth rotation element,and a ninth rotation element; and a fourth planetary gear set includinga tenth rotation element, an eleventh rotation element, and a twelfthrotation element, wherein the input shaft is directly connected with thesecond rotation element, the output shaft is directly connected with theeleventh rotation element, the second rotation element is directlyconnected with the fourth rotation element and the eighth rotationelement, the fifth rotation element is directly connected with thetwelfth rotation element, the sixth rotation element is selectivelyconnectable with each of the first rotation element and the thirdrotation element, the seventh rotation element is selectivelyconnectable with the third rotation element, and the tenth rotationelement is directly connected with the seventh rotation element.
 6. Theplanetary gear train of claim 5, wherein the seventh rotation elementand the ninth rotation element are each selectively connectable with atransmission housing.
 7. The planetary gear train of claim 5, whereinthe first rotation element, the second rotation element, and the thirdrotation element comprise a first sun gear, a first planet carrier, anda first ring gear; the fourth rotation element, the fifth rotationelement, and the sixth rotation element comprise a second sun gear, asecond planet carrier, and a second ring gear; the seventh rotationelement, the eighth rotation element, and the ninth rotation elementcomprise a third sun gear, a third planet carrier, and a third ringgear; and the tenth rotation element, the eleventh rotation element, andthe twelfth rotation element comprise a fourth sun gear, a fourth planetcarrier, and a fourth ring gear.
 8. The planetary gear train of claim 6,further comprising: a first clutch selectively connecting the thirdrotation element and the eleventh rotation element; a second clutchselectively connecting the first rotation element and the sixth rotationelement; a third clutch selectively connecting the third rotationelement and the sixth rotation element; a fourth clutch selectivelyconnecting the third rotation element and the seventh rotation element;a first brake selectively connecting the seventh rotation element andthe transmission housing; and a second brake selectively connecting theninth rotation element and the transmission housing.
 9. The planetarygear train of claim 8, wherein speed shift-stages implemented byselectively operating the first, second, third and fourth clutches andthe first and second brakes include: a first forward speed shift-stage,implemented by operating the third and fourth clutches, and the firstbrake; a second forward speed shift-stage, implemented by operating thefirst and third clutches, and the first brake; a third forward speedshift-stage, implemented by operating the second and third clutches, andthe first brake; a fourth forward speed shift-stage, implemented byoperating the first and second clutches, and the first brake; a fifthforward speed shift-stage, implemented by operating the first, secondand third clutches; a sixth forward speed shift-stage, implemented byoperating the first and second clutches, and the second brake; a seventhforward speed shift-stage, implemented by operating the second and thirdclutches, and the second brake; an eighth forward speed shift-stage,implemented by operating the first and third clutches, and the secondbrake; a ninth forward speed shift-stage, implemented by operating thethird and fourth clutches, and the second brake; a forward tenth speedshift-stage, implemented by operating the first and fourth clutches, andthe second brake; and a reverse-speed shift-stage, implemented byoperating the second and fourth clutches, and the second brake.